Crack Tip Opening Displacement Research Articles

Fracture Toughness Estimate of H-Section Steel for Offshore Structure

In this study, a novel estimating equation based on the WES2808 standard was proposed to predict fracture toughness through the transition temperature of Charpy impact toughness and CTOD (Crack Tip Opening Displacement) fracture toughness. This equation was specifically developed for 460MPa class H-section steel materials used in marine structures, including the base material (BM), heat-affected zone (HAZ), and weld metal (WM). The experimental results confirmed that the proposed estimation equation accurately predicted the fracture toughness across these different material regions. These findings demonstrate the reliability and applicability of the proposed equation in estimated fracture toughness for marine structure materials, thereby contributing to improved safety and performance in harsh environmental conditions.

Comparison of fracture behavior of set concretes based on natural and crushed aggregates

Abstract The studies were carried out to diagnose the effects of coarse aggregate type on the mechanical behavior of plain concretes under incremental loading. During the studies mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (K_Ic^S) and critical crack tip opening displacement (CTODc) were evaluated. Crushed aggregates covered: basalt (BA), granite (GT) and limestone (LM) and natural peeble gravel aggregate (GL) were used in the concrete mixtures. The composite made on pebble aggregate acted as a reference concrete, as it were, in the analysis of the test results. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Both of the analyzed fracture mechanics parameters, i.e. 〖 K〗_Ic^S and CTODc increased significantly in the case of concretes which were manufactured based on crushed aggregates. They amounted in comparison to concrete based on gravel aggregate at levels ranging from 20% for concrete with limestone aggregate, to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. Moreover, a clear correlation in the changes in the obtained results between the main strength parameters and fracture mechanics parameters was observed. The fracture process in each series of concrete was: quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregate. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Effect of Coarse Aggregate Type on the Fracture Toughness of Ordinary Concrete

This research work aims to compare the strength and fracture mechanics properties of plain concretes, obtained from different coarse aggregates. During the study, mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (KIcS) and critical crack tip opening displacement (CTODc) were evaluated. The effect of the aggregates used on the brittleness of the concretes was also analyzed. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Crushed aggregates covered were basalt (BA), granite (GT), and limestone (LM), and natural peeble gravel aggregate (GL) were used in the concrete mixtures. Fracture toughness tests were performed on an MTS 810 testing machine. Due to the high strength of the rock material, the rough surface of the aggregate grains, and good bonding in the ITZ area between the aggregate and the paste, the concretes with crushed aggregates exhibited high fracture toughness. Both of the analyzed fracture mechanics parameters, i.e., KIcS and CTODc, increased significantly in the case of concretes which were manufactured with crushed aggregates. They amounted, in comparison to concrete based on gravel aggregate, to levels ranging from 20% for concrete with limestone aggregate to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. On the other hand, the concrete with gravel aggregate showed the lowest fracture toughness because of the smooth surface of the aggregate grains and poor bonding between the aggregate and the cement paste. However, the fracture process in each series of concrete was quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregates. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Fracture characteristics and microscopic mechanism of slag-based marine geopolymer mortar prepared with seawater and sea-sand

This study utilized seawater, sea sand, and ternary solid waste to produce marine geopolymer mortar (MGM). 23 groups of MGM samples with varying alkali content and basalt fiber (BF) and polypropylene fiber (PPF) volume fractions, as well as marine cement mortar (MCM), were tested for fracture characteristics. Three initial crack length ratios (a0/h) (0.2, 0.3, and 0.4) were designed. The analysis included load-crack mouth opening displacement (P-CMOD) curves for all specimens, focusing on critical crack length (ac), critical crack tip opening displacement (CTODc), fracture toughness (KSIC), fracture energy (GF), and facture brittleness index (FBI). Results indicated that increasing alkali content enhanced strength and elastic modulus, peak fracture load, critical crack extension length (Δac), and CTODc, while decreasing final CMOD. This was attributed to the increased alkali content, which enhanced the mortar’s density. However, excessive alkali content also led to increased shrinkage damage within the matrix, making it prone to stress concentrations and resulting in brittle failure. Based on the research, it is recommended that the alkali content be controlled within the range of 4–5 %. Hybrid fibers showed superior overall toughness enhancement, increasing KSIC, GF, and FBI by 54.3 %, 95.6 %, and 427.4 %, respectively. This improvement was due to the synergistic effect of BF and PPF, which increased the specimen’s elastic modulus, reduced crack propagation speed, and sustained load-bearing capacity during the later stages of crack development. The fracture toughness of conventional geopolymer mortar was positively correlated with the Ca/Si ratio and was lower than that of MGM. In contrast, MGM’s Ca/Si ratio showed an inverse correlation with KSIC, indicating that phase assemblage governs the fracture resistance of MGM. This is because Cl- in seawater intensified geopolymerization reactions. Interwoven gel structures in MGM, with surface depositions like magnesium aluminosilicate hydrate (M-A-S-H), magnesium silicate hydrate (M-S-H), and silica gel, filled pores, and improved homogeneity, resulting in its superior fracture toughness over conventional geopolymer mortar.

Coupled effect of microstructure heterogeneity and hydrogen on local embrittlement of CGHAZ and IC-CGHAZ in X65 pipeline steel

The local embrittlement of the coarse-grained heat-affected zone (CGHAZ) and intercritically reheated CGHAZ (IC-CGHAZ) in X65 pipeline steel was investigated using an in situ crack-tip opening displacement test in air and H2S, combined with microstructure-based simulation. The IC-CGHAZ exhibited significantly lower cracking resistance, with the fracture toughness reduced by 50% compared to CGHAZ in both environments (0.160 mm in air and 0.017 mm in H₂S for IC-CGHAZ, compared to 0.307 mm in air and 0.034 mm in H₂S for CGHAZ). The martensite/austenite (M/A) constituents showed exceptionally higher intrinsic hardness than the ferrite matrix. The continuous distribution of M/As along the prior austenite grain boundaries resulted in local hardening and the formation of heterogeneous hard zones in IC-CGHAZ. Such microstructure heterogeneity resulted in the unique partitioning of plastic strain localization and stress triaxiality that promotes premature fracture, particularly with the coupled effect of hydrogen. This study provides a novel perspective on the fracture mechanisms and the typical fracture morphology of IC-CGHAZs in pipeline steel under the coupled effect of microstructure heterogeneity and hydrogen.

Correlation between heterogeneous micromechanical properties and fracture toughness in X80 girth weld

The safety accidents caused by the service of pipelines will cause huge economic losses due to the deterioration of the fracture toughness of the girth weld. To clarify the fracture behaviors of girth weld, X80 girth welds with heterogeneous microstructure consisted acicular ferrite (AF) and grain boundary ferrite (GBF) with different micromechanical properties were investigated. The results show that the typical microstructure of X80 girth weld is heterogeneous, which is consist of high strength AF and low strength GBF. With the decrease of the difference in micromechanical properties between AF and GBF, the crack tip opening displacement of three girth welds is 0.13 ± 0.04 mm, 0.18 ± 0.04 mm and 0.29 ± 0.05 mm. Meanwhile, the type of microcracks gradually changed from secondary cracks with GBF aggregation to micro-voids without obvious aggregation, which means the fracture mechanism transforms from cleavage fracture to micro-voids aggregation fracture. The finite element analysis indicates that the change of fracture mechanism is mainly due to the reduction of the gap between the micromechanical properties of AF and GBF, the stress and strain distribution are homogenized, resulting the fracture toughness is significantly improved.

Mode II fracture behavior of glass fiber composite-steel bonded interface–experiments and CZM

The dominant failure mode was characterized as debonding in the novel non-welded wrapped composite joint made with GFRP composites wrapped around steel sections. Glass fiber composite-steel three-point end notched flexure (3ENF) and four-point end notched flexure (4ENF) specimens were utilized to experimentally investigate mode II fracture behavior of this composite-steel bonded interface. Two new methods were proposed with the help of digital image correlation (DIC) technique to quantify fracture data during the tests: 1) the “shear strain scaling method” to quantify the crack length a; 2) the asymptotic analysis method based on the longitudinal displacement distribution along the height of the specimen at the pre-crack tip to quantify the crack tip opening displacement (CTOD). To numerically simulate the mode II fracture behavior, a four-linear traction-separation law was proposed in the cohesive zone modeling (CZM) where the softening behavior with a plateau was defined by the authors between traditionally considered initiation and fiber bridging behavior. The experimental and numerical approaches were validated mutually through good matches between the test and FEA results. 3ENF test provided good insight into softening behavior while 4ENF contributed to quantification of fiber bridging. These findings contribute to a more comprehensive characterization and understanding of the ductile fracture behavior of bi-material bonded joints, especially in mode II failure scenarios.

Influence of bedding on fracture toughness and failure patterns of anisotropic shale

The initiation and propagation of hydraulic fractures are closely related to the fracture ability of rocks. Such processes in shale reservoirs are, to a certain extent, controlled by bedding. However, the control mechanism of bedding on the anisotropy of fracture toughness and fracturing behavior remains unclear. In this study, a series of numerical notched semi-circular bend (NSCB) tests are conducted using the discrete element method (DEM) to investigate the influence of bedding properties on the anisotropy of fracture toughness and fracture patterns. Based on the DEM framework, a novel simulation method is proposed to accurately identify two key fracture indicators, the fracture process zone (FPZ) and crack tip opening displacement (CTOD), to reveal the fracture driving mechanism. The results show that the fracture toughness of shale is negatively correlated with bedding angles β but positively correlated with bedding spacing and bedding strength. Both the bedding strength and spacing significantly influence the fracture pattern of the specimens with β = 0°–60°, whereas the specimen with β = 90° is scarcely affected by the bedding planes. The evolution of the CTOD and FPZ in shale exhibits distinct phased characteristics. Due to the strong suppression effect of low-angle bedding planes on pre-peak crack deflection, the CTOD and FPZ exhibit opposite trends with respect to bedding angles before and after the peak load. This study facilitates the understanding of the fracture propagation process of anisotropic shale and could provide guidance for hydraulic fracturing design in shale reservoirs.

Investigation of the fracture characteristics of mixed-mode I/III crack by using two kinds of sandstone specimens

This study aims to identify specimens that are more suitable for examining the failure properties of I/III mixed-mode cracks under static loads. We employed single-edge notched bending (SENB) and edge-notched disc bending (ENDB) specimens, and used ABAQUS finite element method software to calculate the stress intensity factors for modes I and III at various crack inclination angles θ. Fracture toughness was tested using three-point bending experiments on two types of sandstone specimens. The evolution of mixed-mode I/III fracture morphology and failure patterns was investigated with a monocular microscope. Additionally, the evolution of the strain field and crack tip opening displacement was analyzed using the digital image correlation method. Our findings indicate that the fracture toughness of the ENDB specimens surpassed that of the SENB specimens. The effective fracture toughness of both SENB and ENDB specimens initially increased with crack inclination angle θ but then decreased. The fracture mode correlated with energy release; the energy release rate of the ENDB specimens exceeded that of the SENB specimens, making the former more brittle. For SENB specimens, crack initiation was primarily intergranular, while ENDB specimens exhibited predominantly transgranular fractures. The crack initiation moments for both specimen types increased with higher crack inclination angles. Furthermore, at the same crack inclination angle, ENDB specimens cracked earlier than SENB specimens.

A new understanding of hydrogen-assisted cracking of coarse-grained heat-affected zone in X65 pipeline steel through {110} lath bainite boundary texture

The susceptibility of subzones of the coarse-grained heat-affected zone (CGHAZ) in X65 pipeline steel to hydrogen embrittlement was studied through an in situ crack-tip opening displacement test in an H2S-containing environment. The intercritically reheated CGHAZ (IC-CGHAZ) exhibited the highest embrittlement factor of 89.4%, compared to 64.0% for the sub-critically reheated CGHAZ (SC-CGHAZ). Hydrogen transportation by dislocations to massive-slender martensite/austenite (M/A) constituents initiated cracks in IC-CGHAZ. Deterioration of lath bainite (LB) boundaries, with separation of M/A-ferrite interface, accelerated crack propagation across prior austenite grains and promoted hydrogen-assisted degradation of fracture toughness. Reheated CGHAZ at a peak temperature of 620 °C led to an increased intensity of the {110} LB boundary texture by up to 52% in SC-CGHAZ. This enhanced texture facilitated dislocation slipping along {110} LB boundary planes, thereby promoting deformation compatibility and preventing the deterioration of LB boundaries in the presence of hydrogen.

Two-way coupled modeling of dislocation substructure sensitive crystal plasticity and hydrogen diffusion at the crack tip of FCC single crystals

Dislocation substructure-sensitive crystal plasticity (DSS-CP) modeling accounts for the evolution of mesoscale structures using dislocation-based parameters informed by experiments and computation at various lower length scales. To a first-order approximation, DSS-CP model parameters are affected by hydrogen (H) concentration, accounting for both H-dependent yield strength and strain hardening rate. This H-affected DSS-CP model is two-way coupled with H-diffusion to explore both effects of plastic deformation on H-diffusion and effects of H on yield strength and strain hardening in the DSS-CP model. Crack tip simulations are performed for face-centered cubic (FCC) metals under monotonic loading conditions with and without H. Enhanced maximum plastic deformation in the vicinity of the crack tip (i.e., localization or intensification of plastic strain) and crack tip opening displacement (CTOD) are predicted in the presence of H, consistent with experimental observations. In spite of increased initial strength due to H, subsequent reduction of the rate of strain hardening in the presence of H is shown to enhance localization of crack tip plasticity. Furthermore, this modeling framework predicts that higher H-diffusivity (leading to a larger H-affected zone) will enhance the crack tip plasticity, making use of the two-way coupling algorithm implemented in this work. On the other hand, we find that the H-sensitivity of crack tip strain localization response, based only on modification of model parameters, is too weak to explain typical experimental observations. This points to the need to develop more advanced DSS-CP constitutive relations that consider highly complex dislocation interactions with point defects.

Fracture evolution characteristics of asphalt concrete using digital image correlation and acoustic emission techniques

The cracking damage of asphalt concrete significantly affects the service life of pavement. The objective of this research is to investigate fracture mechanisms of asphalt concrete by employing a synergistic approach combining digital image correlation (DIC) and acoustic emission (AE) techniques under three-point bending tests. Firstly, the crack tip opening displacement (CTOD) and the fracture process zone (FPZ) derived from DIC were utilized to classify fracture stages and describe the entire crack propagation process. Meanwhile, AE-related parameters were applied to detect the internal damage and fracture characteristics. Subsequently, the results from DIC and AE were utilized for comparative analysis to evaluate the cracking resistance of different materials. Finally, the fractal dimension and AE b-value were used to distinguish the characteristics of the critical damage conditions. The results indicated that both techniques are effective in classifying the fracture stage of asphalt concrete. DIC can visualize and analyze crack propagation processes and paths on concrete surfaces, especially at the stage of macrocrack initiation and propagation. AE allows for continuous monitoring and highly sensitive detection of early-stage damage inside concrete. The distinct advantages of DIC and AE result in different fracture stage identification results at the early stage, but consistent after the appearance of macrocracks. Based on the relationship between CTOD and AE cumulative count, a simple approach is proposed to directly evaluate the cracking resistance of different asphalt concretes. The formation of macrocracks in asphalt concrete can be reflected by a shift where the correlation dimension drops steeply to the minimum value, and a minimum inflection point in the AE b-value curve acts as a precursor of complete fracture. The research offers an in-depth insight of both surface deformation and internal damage, thus enhancing the understanding of crack growth behavior and fracture process in asphalt concrete.

Liquid Hydrogen Properties Affecting Fracture Toughness

In this study, fracture toughness with the base metal of 9% Ni steel, a cryogenic steel, was evaluated under conditions without hydrogen charging (WO-H) and with hydrogen charging (W-H). Hydrogen charging was performed using an electrochemical cathodic charging method in a electrolyte of 3% NaCl + 0.3% NH4SCN at 19℃ with a current density of 50 A/m². Fracture toughness was assessed at -80℃, -100℃, -130℃, and -160℃ using CTOD (Crack Tip Opening Displacement) tests. The results for WO-H indicated a decrease in fracture toughness values with decreasing temperature, while the results for W-H showed an increase in fracture toughness values as the temperature decreased. In addition, the fracture surfaces and fracture toughness of WO-H and W-H became increasingly similar as the temperature decreased, as observed through scanning electron microscopy (SEM). At -80℃, there was a significant difference in fracture toughness between the WO-H and W-H conditions. WO-H was influenced only by the low temperature, whereas W-H was affected by both low temperature and hydrogen, showing combined effects that led to a decrease in fracture toughness due to hydrogen embrittlement. However, at -160℃, the fracture toughness values for both WO-H and W-H conditions were nearly identical. This suggests that the temperature effect on fracture toughness reduction is greater than hydrogen embrittlement at very low temperatures.

Determination of Fracture Mechanic Parameters of Concretes Based on Cement Matrix Enhanced by Fly Ash and Nano-Silica.

This study presents test results and deep discussion regarding measurements of the fracture toughness of new concrete composites based on ternary blended cements (TCs). A composition of the most commonly used mineral additive (i.e., fly ash (FA)) in combination with nano-silica (NS) has been proposed as a partial replacement of the ordinary Portland cement (OPC) binder. The novelty of this article is related to the fact that ordinary concretes with FA + NS additives are most often used in construction practice, and there is a decided lack of fracture toughness test results concerning these materials. Therefore, in order to fill this gap in the literature, an extensive evaluation of the fracture mechanic parameters of TC was carried out. Four series of concretes were created, one of which was the reference concrete (REF), and the remaining three were TCs. The effect of a constant content of 5% NS and various FA contents, such as 0, 15%, and 25% wt., as a partial replacement of cement was studied. The parameters of the linear and nonlinear fracture mechanics were analyzed in this study (i.e., the critical stress intensity factor (KIcS), critical crack tip opening displacement (CTODc), and critical unit work of failure (JIc)). In addition, the main mechanical parameters (i.e., the compressive strength (fcm) and splitting tensile strength (fctm)) were evaluated. Based on the studies, it was found that the addition of 5% NS without FA increased the strength and fracture parameters of the concrete by approximately 20%. On the other hand, supplementing the composition of the binder with 5% NS in combination with the 15% FA additive caused an increase in all mechanical parameters by approximately another 20%. However, an increase in the FA content in the concrete mix of another 10% caused a smaller increase in all analyzed factors (i.e., by approximately 10%) compared with a composite with the addition of the NS modifier only. In addition, from an ecological point of view, by utilizing fine waste FA particles combined with extremely fine particles of NS to produce ordinary concretes, the demand for OPC can be reduced, thereby lowering CO2 emissions. Hence, the findings of this research hold practical importance for the future application of such materials in the development of green concretes.

Study on crack propagation behaviors of three-point bending concrete beams with small span-depth ratios

Three-point bending (TPB) beams with small span-depth ratios, i.e. TPB beams with the same span of 400 mm but various depths (100 mm, 150 mm and 200 mm), were tested to study the crack propagation behaviors of concrete. The evaluations of crack extension resistance curve (KR-curve), fracture process zone (FPZ) length, lFPZ, and crack tip opening displacement (CTOD) were studied. The digital image correlation (DIC) technique was utilized to monitor the entire loading process. Moreover, the effects of strain rates (10−5/s, 10−4/s, 10−3/s and 10−2/s) on the fracture process of TPB beams with small span-depth ratios (2, 2.5 and 3) were discussed based on findings in literature. The results shown that (1) with the increase of specimen depth from 100 mm to 200 mm, the obtained KR-curves and initial fracture toughness were not influenced by the small span-depth ratios, while different increase trends were observed for the unstable fracture toughness, the average maximum value of lFPZ and the value of CTOD. (2) With the loading rate increasing from 10−5/s to 10−2/s, the obtained KR-curve and the maximum length of FPZ increased slightly, while the evolution of CTOD was not affected by the loading rate.

An experimental study on mechanical and fracture characteristics of hybrid fibre reinforced concrete

This research investigates the impact of polypropylene and glass fibres on the mechanical and fracture properties of concrete. Prepared specimens consisted of plain concrete (PC), polypropylene fibre-reinforced concrete (PPFC), glass fibre-reinforced concrete (GFC), and polypropylene-glass hybrid fibre-reinforced concrete (HFC). The specimens were evaluated for their mechanical and fracture properties. PPFC indicated a little drop in compressive strength and GFC demonstrated a moderate gain; HFC, as a result of synergistic effect of polypropylene fibre and glass fibre, demonstrated a marginal increase in compressive strength. The substantial increase in flexural and split tensile strength was observed in all the fibre reinforced concrete specimens, compared to plain concrete. The incorporation of polypropylene fibre yields the greatest improvement in concrete's split tensile strength, whereas the incorporation of glass fibres results in the highest improvement in concrete's flexural strength. The fracture characteristics also showed significant improvement in fibre incorporated concrete. The coaction of polypropylene and glass fibre in HFC resulted in 30.1 % increase in first crack strength and a threefold rise in flexural toughness compared to plain concrete. Compared to plain concrete, the critical crack tip opening displacement of PPFC, GFC, and HFC increased by 43.90 %, 26.25 %, and 39.02 %, while the critical stress intensity factor increased by 15.73 %, 13.10 %, and 14.22 %. Subsequently, it was determined that the fracture energies of PPFC, GFC, and HFC were 3.35, 1.78, and 2.50 times those of PC, respectively. In addition, the synergistic effect of polypropylene and glass fibres in concrete was studied, and it was found that when used together, the fibres have better fracture characteristics than when used alone, without compromising mechanical strength. Subsequently, different bilinear softening curves were used to predict fracture parameters, and it was seen that the computed values agreed with the experimental values.

Fracture toughness and microstructural analysis of rotary friction welded S355J2 and SS316L steels for critical applications

Dissimilar metal welding is seeing growing adoption across industries to enhance structural functionality and efficiency. Achieving high-quality, defect-free dissimilar weld joints requires a comprehensive understanding of the interrelationships between the welding-induced microstructural changes and the material's performance characteristics, particularly its fracture-related properties. This study investigates the impact of microstructural changes on the fracture toughness of dissimilar welds between structural low-carbon steel (S355J2) and austenitic stainless steel (SS316L) prepared using the Rotary Friction Welding (RFW) technique. Welding preforms were created from respective pipe pup pieces. The evaluation involves microstructural analysis, tensile testing, hardness testing, and fracture toughness testing using compact tension specimens derived from various zones of the weld joints. Results revealed significant microstructural differences across the weld joint. The weld region exhibited stable hardness with a maximum of 208 HV1 in S355J2′s thermo-mechanically affected zone (TMAZ). High tensile strength (Ultimate Tensile Strength 540 MPa, Yield Strength 367 MPa) with failures mainly on the S355J2 side. The fracture toughness (KQ) matched parent metal values, with the RFW weld centre line (WCL) showing superior crack tip opening displacement (CTOD) of 0.35 mm. Fractography generally indicates ductile failure.

The influence of temperatures on the mechanical properties and fracture behavior of rocks under mixed mode I/II loading

A comprehensive understanding of the fracture behavior of pre-heated rocks under to mixed mode I/II loading is crucial for deep underground engineering. The effect of high temperature on the fracture process zone (FPZ) and fracture toughness of rocks was experimentally investigated using semi-circular bend (SCB) samples. Surface displacement and associated strain field under loading were captured using digital image correlation. The results showed that the mechanical properties of SCB samples gradually decreased with increasing temperature. Rocks exposed at temperature exceeding 600 °C demonstrated a significant reduction in peak load, generalized stiffness, fracture toughness, and absorbed energy. Moreover, the load–displacement curves and macroscopic fracture characteristics of pre-heated SCB samples revealed a transition from brittleness to ductility with increasing temperature under mixed mode I/II loading. Both the length and width, as well as the crack tip opening displacement of the FPZ, increased with rising temperature. At lower temperatures (25 ∼ 400 °C), the ratio of FPZ length to width typically ranged between 2 and 3. While, at elevated temperature (600 ∼ 1000 °C), this ratio expanded to between 3 and 4. The initiation of thermally induced cracks in rocks will accelerate damage evolution under mixed mode I/II loading, as indicated by the development of the maximum principal strain with displacement. Scanning electron microscopy and polarization microscopy images of the microscopic fracture morphology in pre-heated rocks illustrated isolated and dispersed microcracks appeared at lower temperatures, whereas at elevated temperatures, intricate microcrack networks and broken grains were observed.

A prediction model of brittle crack arrest toughness in TMCP heavy plates

Micro-alloyed low carbon MnCrNiCuMo steels were proposed to produce heavy plates with a maximum thickness of 100 mm. An integrated industrial route including a thermo-mechanical control process (TMCP) based on a study on continuous cooling transformation was applied in industrial production. Comprehensive mechanical properties tests including the measurement on resistance against crack initiation using crack tip opening displacement (CTOD) approach were conducted. Large scale wide-plate temperature gradient double tension (DT) technique was employed to evaluate the crack arrest toughness Kca in the heavy plates under different conditions. Nil-ductility transition temperature (NDTT) was also tested across the entire thickness section of the plates. The results showed that heavy steel plates were qualified being brittle crack arrest (BCA) products at EH47 grade with yield strength high than 460 MPa. High crack initiation toughness was exhibited by both Charpy-V notch impact property and CTOD values. Crack arrest toughness at −10 °C greater than 253 MPa √m was achieved in a plate even with thickness of 100 mm. The mean value of crack arrest toughness at different temperature measured by the DT approach can be indexed by the highest NDTT in the interior section of the heavy plates leading to an empirical prediction model. Further, fracture mechanics based master curve approach was used to statistically predict crack arrest toughness distribution over a wide range of temperatures showing improved predictability over the empirical model and an existing model in the literature.

Experimental Research on the Low-Cycle Fatigue Crack Growth Rate for a Stiffened Plate of EH36 Steel for Use in Ship Structures

This paper presents a straightforward approach for determining the low-cycle fatigue (LCF) crack propagation rate in stiffened plate structures containing cracks. The method relies on both the crack tip opening displacement (CTOD) and the accumulative plastic strain, offering valuable insights for ship structure design and assessing LCF strength. Meanwhile, the LCF crack growth tests for the EH36 steel were conducted on stiffened plates with single-side cracks and central cracks under different loading conditions. The effects of stress amplitude, stress ratio, and stiffener position on the crack growth behavior were examined. Fitting and verifying analyses of the test data were employed to investigate the relationship between CTOD and the crack growth rate of EH36 steel under LCF conditions. The results showed that the proposed CTOD-based prediction method can accurately characterize the LCF crack growth behavior for stiffened plate of EH36 steel for use in ship structures.